U.S. patent application number 14/920503 was filed with the patent office on 2016-02-11 for fuel cell having perforated flow field.
The applicant listed for this patent is Ford Motor Company. Invention is credited to Shinichi Hirano, Alireza Pezhman Shirvanian.
Application Number | 20160043411 14/920503 |
Document ID | / |
Family ID | 42934656 |
Filed Date | 2016-02-11 |
United States Patent
Application |
20160043411 |
Kind Code |
A1 |
Shirvanian; Alireza Pezhman ;
et al. |
February 11, 2016 |
FUEL CELL HAVING PERFORATED FLOW FIELD
Abstract
A fuel cell system includes a bipolar plate having a flow field
formed therein. The flow field is partially defined by at least two
adjacent channel portions separated by a wall portion. The wall
portion includes a surface at least partially defining a passageway
between the channel portions. The passageway may be sized so as to
create a pressure difference between the channel portions. The
pressure difference may draw at least a portion of a liquid droplet
obstructing one of the channel portions toward and into the
passageway.
Inventors: |
Shirvanian; Alireza Pezhman;
(Ann Arbor, MI) ; Hirano; Shinichi; (West
Bloomfield, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Ford Motor Company |
Dearborn |
MI |
US |
|
|
Family ID: |
42934656 |
Appl. No.: |
14/920503 |
Filed: |
October 22, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12421025 |
Apr 9, 2009 |
9178230 |
|
|
14920503 |
|
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Current U.S.
Class: |
429/457 |
Current CPC
Class: |
H01M 8/04179 20130101;
H01M 8/026 20130101; H01M 8/04156 20130101; H01M 8/241 20130101;
H01M 8/0297 20130101; H01M 8/0267 20130101; H01M 8/04171 20130101;
H01M 2008/1095 20130101; Y02E 60/50 20130101; H01M 8/0258 20130101;
H01M 8/2457 20160201 |
International
Class: |
H01M 8/02 20060101
H01M008/02 |
Claims
1-8. (canceled)
9. A fuel cell comprising: a flow-field plate defining at least two
adjacent channel portions and a wall portion separating the channel
portions, the wall portion having perforations therein that are
textured or coated such that surface tension gradients between the
channel portions and perforations draw liquid droplets obstructing
the channel portions into the perforations.
10. (canceled)
11. The fuel cell of claim 9, wherein at least one of the
perforations is completely formed within the wall portion.
12. The fuel cell of claim 9, wherein each of the channel portions
has a hydraulic diameter and wherein a spacing of the perforations
depends on the hydraulic diameter.
13-20. (canceled)
21. A fuel cell comprising: a bipolar plate having a flow field
partially defined by at least two adjacent channels separated by a
wall that includes a surface at least partially defining a
passageway between the channels and being textured or coated such
that a surface tension gradient between the surface and one of the
channels draws a liquid droplet obstructing the one of the channels
into the passageway.
22. The fuel cell of claim 21 further comprising a membrane
electrode assembly in contact with the bipolar plate and at least
partially defining the passageway.
23. The fuel cell of claim 21, wherein the passageway is completely
formed within the wall.
24. The fuel cell of claim 21, wherein the passageway is V-shaped,
U-shaped, round or polygonal.
25. The fuel cell of claim 21, wherein the passageway has a
hydraulic radius and at least one of the channels has a hydraulic
radius and wherein the hydraulic radius of the passageway is less
than one half the hydraulic radius of the at least one channel.
26. The fuel cell of claim 21, wherein a size of the passageway
depends on at least one operating parameter of the fuel cell
system.
27. A fuel cell comprising: a flow-field plate defining at least
two adjacent channel portions and a wall portion separating the
channel portions, the wall portion having perforations configured
to draw liquid droplets obstructing the channel portions into the
perforations.
28. The fuel cell of claim 27, wherein at least one of the
perforations is completely formed within the wall portion.
29. The fuel cell of claim 27, wherein each of the channel portions
has a hydraulic diameter and wherein a spacing of the perforations
depends on the hydraulic diameter.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional of application Ser. No.
12/421,025, filed Apr. 9, 2009, the disclosure of which is hereby
incorporated in its entirety by reference herein.
BACKGROUND
[0002] 1. Field
[0003] The invention relates to fuel cells having perforated flow
fields.
[0004] 2. Discussion
[0005] A fuel cell is an electrochemical conversion device that
produces electricity from a fuel and oxidant that react in the
presence of an electrolyte.
[0006] Referring now to FIG. 1, a prior art fuel cell 10 includes a
membrane electrode assembly (MEA) 12 sandwiched between a pair of
flow-field plates 14, 16. The MEA 12 includes a proton exchange
membrane (PEM) 18 and catalyst layers 20, 22 bonded to opposite
sides of the PEM 18. The MEA 12 further includes gas diffusion
layers 24, 26 (anode, cathode respectively) each in contact with
one of the catalyst layers 20, 22. As apparent to those of ordinary
skill, the gas diffusion layer 24 and catalyst layer 20 may
collectively be referred to as an electrode. Likewise, the gas
diffusion layer 26 and catalyst layer 22 may also collectively be
referred to as an electrode.
[0007] The flow-field plate 14 includes at least one channel 28n.
As known in the art, the at least one channel 28n may form a
spiral, "S," or other shape on the face of the flow-field plate 14
adjacent to the anode 24. Hydrogen from a hydrogen source (not
shown) flows through the at least one channel 28n to the anode 24.
The catalyst 20 promotes the separation of the hydrogen into
protons and electrons. The protons migrate through the PEM 18. The
electrons travel through an external circuit 30 to produce
electrical power.
[0008] The flow-field plate 16 also includes at least one channel
32n. Similar to the at least one channel 28n, the at least one
channel 32n may form a spiral, "S," or other shape on the face of
the flow-field plate 16 adjacent the cathode 26. Oxygen from an
oxygen or air source (not shown) flows through the at least one
channel 32n and to the cathode 26. The hydrogen protons that
migrate through the PEM 18 combine with the oxygen and electrons
returning from the external circuit 30 to form water and heat.
[0009] As apparent to those of ordinary skill any number of fuel
cells 10 may be combined to form a fuel cell stack (not shown).
Increasing the number of cells 10 in a stack increases the voltage
output by the stack. Increasing the surface area of the cells 10 in
contact with the MEA 12 increases the current output by the
stack.
SUMMARY
[0010] A fuel cell system includes a bipolar plate having a flow
field formed therein. The flow field is partially defined by at
least two adjacent channel portions separated by a wall portion.
The wall portion includes a surface at least partially defining a
passageway between the channel portions. The passageway is sized so
as to create a pressure difference between the channel portions.
The pressure difference draws at least a portion of a liquid
droplet obstructing one of the channel portions toward and into the
passageway.
[0011] A fuel cell system includes a pair of flow-field plates and
a membrane electrode assembly sandwiched between the flow-field
plates. At least one of the flow-field plates includes a surface
defining at least two adjacent channel portions and a wall portion
separating the channel portions. The channel portions are
configured to deliver a fluid to the membrane electrode assembly.
The wall portion has perforations that create a pressure difference
between the channel portions. The pressure difference moves a
liquid droplet obstructing one of the channel portions through the
one channel portion.
[0012] An automotive fuel cell stack includes a plurality of fuel
cells. Each of the fuel cells includes at least one flow-field
plate having a flow field at least partially defined by two
adjacent channel portions separated by a wall portion. The wall
portion includes a surface at least partially defining a passageway
between the channel portions. The passageway is at least one of
shaped, textured and coated so as to create a surface tension
gradient between the surface at least partially defining the
passageway and a surface of one the channel portions obstructed by
a liquid droplet. The surface tension gradient draws at least a
portion of the liquid droplet into the passageway.
[0013] While certain embodiments in accordance with the invention
are illustrated and disclosed, such disclosure should not be
construed to limit the invention. It is anticipated that various
modifications and alternative designs may be made without departing
from the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a side view, in cross-section, of a portion of a
prior art fuel cell.
[0015] FIG. 2 is a plan view of a portion of a flow-field plate of
FIG. 1.
[0016] FIGS. 3A and 3B are plan views of a portion of a flow-field
plate according to an embodiment of the invention.
[0017] FIGS. 4A through 4C are plan views of a computational fluid
dynamic model of a portion of another flow-field plate at several
simulated instances of time.
[0018] FIG. 5 is an end view of a portion of a fuel cell according
to an embodiment of the invention.
[0019] FIG. 6 is a side view, in cross-section, of the fuel cell of
FIG. 5 taken along line 6-6 of FIG. 5.
[0020] FIG. 7 is an end view of a portion of a fuel cell according
to another embodiment of the invention.
[0021] FIG. 8 is a side view, in cross-section, of the fuel cell of
FIG. 7 taken along line 8-8 of FIG. 7.
DETAILED DESCRIPTION
[0022] Referring now to FIG. 2, the flow-field plate 16 includes
several parallel channels 32n, i.e., 32a, 32b, 32c. The channels
32n are separated by wall portions 34. In the illustration of FIG.
2, the flow of oxygen is indicated by arrow.
[0023] A droplet of water 36 has condensed and filled the entire
cross-section of the channel 32b thus obstructing the flow of
oxygen downstream of the droplet 36. This flooding of the channel
32b may affect the durability of the fuel cell 10, may cause
non-uniform distribution of reactants to the channels 32n, may
cause non-uniform current generation by the fuel cell 10 and/or may
affect the performance of the fuel cell 10.
[0024] The flooding of channel 32 b may also promote flooding in
the channels 32a, 32c. The stagnant zone downstream of the droplet
36 may generate an increased electrical load for other active areas
thus making water generation and flooding more probable in these
otherwise active areas. This propagation of flooding may affect the
operation of the fuel cell 10.
[0025] Referring now to FIGS. 3A and 3B, an embodiment of a
flow-field plate 38 includes substantially parallel channels 40n,
i.e., 40a, 40b, 40c. In other embodiments, a fewer or greater
number of channels 40 n may be used. These channels 40n may form a
spiral, "S," or other desired shape on a face of the flow-field
plate 38 configured to be in contact with a membrane electrode
assembly (MEA) (not shown).
[0026] The channels 40n share a common fluid source (not shown) and
fluid sink (not shown) as known in the art. Oxygen, for example,
may enter the flow-field plate 38 through an "in" port (not shown)
which fluidly communicates with each of the channels 40a, 40b, 40c.
Water and un-reacted oxygen may exit the flow-field plate 38 though
an "out" port (not shown) which also fluidly communicates with each
of the channels 40a, 40b, 40c. Other configurations are also
possible.
[0027] The channels 40n are separated by wall portions 42 (current
collectors, landing areas, etc.) The wall portions 42 include
passageways 44 that fluidly connect adjacent channels 40n. In the
embodiment of FIGS. 3A and 3B, the passageways 44 are formed at
regular intervals along the channels 40n. The passageways 44 may be
formed at intervals from 10 to 100 times the hydraulic diameter,
D.sub.h, of one of the channels 40n (where D.sub.h=4.times.cross
sectional area of the channel/perimeter of the channel). In other
embodiments, the passageways 44 may be formed at irregular
intervals, staggered intervals, in an alternating pattern or as
design considerations dictate. As explained below, the passageways
44 are sized so as to draw condensed water from the channels 40n
into the passageways 44 to reduce and/or prevent flooding of the
channels 40n.
[0028] As illustrated in FIG. 3A, a droplet of water 46 has
condensed and filled the entire cross-section of the channel 40b.
The droplet 46 obstructs the flow of reactants (indicated by
arrow), e.g., oxygen, hydrogen, air, etc., to the MEA (not shown)
downstream of the droplet 46. The passageways 44, however, allow
the reactants to continue flowing though the region of the channel
40b downstream of the droplet 46. This prevents the generation of a
static (stagnant) zone downstream of the droplet 46. Due to lower
pressures in the channels 40a and 40c, and 40b downstream of the
droplet 46 (relative to a pressure in the channel 40b upstream of
the droplet 46), the droplet 46 travels down the channel 40b until
it encounters at least one of the passageways 44. The droplet 46 is
then drawn into these passageways 44.
[0029] As illustrated in FIG. 3B, the droplet 46 illustrated in
FIG. 3A has dispersed into smaller droplets 48 that may be carried
with the flow of oxygen and/or may vaporize by virtue of the high
flow velocity in the channels 40n.
[0030] Referring now to FIGS. 4A through 4C, numbered elements of
FIGS. 4A through 4C that differ by 100 relative to numbered
elements of FIGS. 3A and 3B have similar, although not necessarily
identical, descriptions to the numbered elements of FIGS. 3A and
3B. A computational fluid dynamic model of a flow-field plate 138
includes generally parallel channels 140n, i.e., 140a, 140b, 140c,
140d, separated by wall portions 142. Passageways 144 formed in the
wall portions 142 fluidly connect adjacent channels 140n.
[0031] The passageways 144 are sized so as to create a pressure
gradient that will drive water droplets in the channels 140n toward
and into the passageways 144. For example, the passageways 144 may
have a hydraulic radius of less than half of that for one of the
channels 140n (yet be large enough to avoid issues related to
surface tension and capillary forces that may make purging and
removing water droplets difficult.) If the passageways 144 are too
large (for example, large enough to promote cross-flow, i.e.,
uniform pressure, between the channels 140n), such a pressure
gradient will not exist and water droplets may still form and stall
within the channels 140n.
[0032] Values of the parameters associated with the model are
listed in Table 1. Of course, other values are also possible as
dictated by design and/or performance considerations.
TABLE-US-00001 TABLE 1 Channel Height 787.4 microns Channel Width
1016 microns Passageway Height 500 microns Passageway Width 500
microns Flow Rate 1e-5 kilograms/second Contact Angle 110 degrees
Droplet Thickness 1 millimeter
[0033] As illustrated in FIG. 4A (time=0.024 sec.), the droplet 146
fills the entire cross section of the channel 140c. The droplet 146
starts to be drawn into two of the passageways 144 as illustrated
in FIG. 4B (time=0.028 sec.) As illustrated in FIG. 4C (time=0.032
sec.), the droplet 146 has been removed from the channel 140c and
resides within the two passageways 144 as droplets 148.
[0034] As apparent to those of ordinary skill, the mechanism by
which the droplet 146 enters the passageways 144 is governed by the
transport of mass, momentum, energy, charge and species through the
fuel cell components, such as a gas diffusion layer (not shown) and
catalyst layer (not shown), and the channels 140n.
[0035] The passageways 144 illustrated in FIGS. 4A through 4C are
defined by straight edges. In other embodiments, the edges that
define the passageways 144 may be curved or otherwise shaped as
desired. Certain shapes, textures and/or coatings of the
passageways 144 may create a surface tension gradient between, for
example, a surface defining one of the passageways 144 if adjacent
to the droplet 146 and a surface of the channel 140n in which the
droplet 146 resides. As apparent to those of ordinary skill, design
considerations and operating parameters of the fuel cell, such as
temperature, flow velocity, etc., may influence the selection of
the particular shape, texture and/or coating used.
[0036] The permeability of any porous components, such as the gas
diffusion layer (not shown) and catalyst layer (not shown), and/or
the droplet interaction with the surfaces
(hydrophobicity/hydrophilicity) of the channels 140n and edges of
the passageways 144 may have an effect on the geometric design and
effectiveness of the passageways 144 to remove water. Operating
parameters, such as flow velocity, operating temperature, etc., may
also have an effect on the geometric design and effectiveness of
the passageways 144 to remove water.
[0037] A full multiphase computational fluid dynamic or finite
element study similar to that illustrated in FIGS. 4A through 4C
(or experimentation) may be required to size/design the passageways
144. In lieu of such a study, an analysis based on the Bernoulli
equation may provide some insight into droplet movement.
[0038] The general form of the Bernolli equation is:
p 1 .rho. + 1 2 V 1 2 + gz 1 = p 2 .rho. + 1 2 V 2 2 + gz 2 = const
##EQU00001##
[0039] According to the above, with subscript 1 referring to
quantities in the flooded channel 140c downstream of the droplet
146 (which is stagnant, i.e., flow velocity V.sub.1.apprxeq.0,
z.sub.1=z.sub.2), and subscript 2 referring to quantities in the
channel 140b or 140d we have
p 1 .rho. = p 2 .rho. + 1 2 V 2 2 = const_ 1 ##EQU00002##
[0040] Because V.sub.2.noteq.0 in order for this equality to hold
true, we must have p.sub.1>p.sub.2 which indicates the
generation of a pressure gradient that pushes the droplet 146 from
the flooded channel 140c to at least one of the passageways
144.
[0041] Referring now to FIG. 5, numbered elements of FIG. 5 that
differ by 200 relative to numbered elements of FIGS. 3A and 3B have
similar, although not necessarily identical, descriptions to the
numbered elements of FIGS. 3A and 3B. A fuel cell 250 includes a
corrugated flow-field plate 238 having opposing face portions 252,
254, a contact plate 256 in contact with, and sealed against, the
face portion 252 and an MEA 258 in contact with, and sealed
against, the face portion 254. The corrugated plate 238 and contact
plate 256 define a plurality of channels 260 though which a
coolant, such as water, may flow. The corrugated plate 238 and MEA
258 define a plurality of channels 240 through which a fuel,
reactant, etc., may flow.
[0042] Referring now to FIG. 6, passageways 244n, i.e., 244a, 244b,
244c, are formed within the corrugated plate 238 and extend to the
MEA 258. That is, in the embodiment of FIG. 6, the MEA 238
partially defines the passageways 244n. The passageway 244 a has a
V-shape, the passageway 244b has a U-shape and the passageway 244c
has a polygonal shape. Of course, the passageways 244n may all have
the same shape. Other shapes and positions are also possible.
[0043] Referring now to FIG. 7, numbered elements of FIG. 7 that
differ by 300 relative to numbered elements of FIGS. 3A and 3B have
similar, although not necessarily identical, descriptions to the
numbered elements of FIGS. 3A and 3B. A fuel cell 350 includes a
flow-field plate 338 having opposing face portions 352, 354, a
cooling plate 356 in contact with, and sealed against, the face
portion 352 and an MEA 358 in contact with, and sealed against, the
face portion 354. A plurality of channels 360 are formed within the
cooling plate 356. The channels 360 deliver a coolant, such as
water, to the face portion 352 to cool the flow-field plate 338. A
plurality of channels 340 are formed within the flow-field plate
338. The channels 340 deliver a fuel, reactant, etc., to the MEA
358.
[0044] Referring now to FIG. 8, passageways 344n, i.e., 344a, 344b,
344c, 344d are formed within the flow-field plate 338. The
passageways 344a, 344b, 344c extend to the MEA 358. The passageway
344d is formed completely within the flow-field plate 338. Other
embodiments, such as the embodiment of FIGS. 5 and 6, may also
include passageways completely formed within the flow-field plate.
(If passageways are formed entirely within the corrugated plate 238
illustrated in FIG. 6, adjacent channels 240 may be connected by
small pipes or tubes to prevent the coolant from leaking into the
channels 240.)
[0045] The passageway 344a has a V-shape, the passageway 344b has a
U-shape, the passageway 344c has a polygonal shape and the
passageway 344d has a round shape. Of course other shapes and
positions are also possible.
[0046] While embodiments of the invention have been illustrated and
described, it is not intended that these embodiments illustrate and
describe all possible forms of the invention. The words used in the
specification are words of description rather than limitation, and
it is understood that various changes may be made without departing
from the spirit and scope of the invention.
* * * * *